Thermodynamic investigations of fuel-cladding chemical interaction in U-5Fs and U-10Zr metallic fuels with the TAF-ID

Fuel-Cladding Chemical Interaction (FCCI) in metallic nuclear fuels is a key phenomenon that limits the maximum burn-up and operating power as it can cause premature failure of the fuel cladding. Therefore, being able to accurately predict the interactions of the fuel-cladding system by means of thermodynamic calculations contributes to our understanding of how to mitigate this failure mechanism. In order to test the capabilities of the Thermodynamic of Advanced Fuels – International Database (TAF-ID) to predict these interactions, calculations have been performed on two irradiated metallic fuels: U-5Fs in SS316 cladding and U-10Zr in HT9 cladding, for which experimental observations are available in the literature. TAF-ID calculations have allowed the confirmation of some of the phases that were observed during experimental characterizations and the identification of unknown ones: Particularly for the U-5Fs fuel, two primary Fe-rich phases have been predicted: (i) FeU6, that extends up to 120 μm into the fuel, and (ii) UFe2 with >30 wt.% Fe, likely to be the Fe-rich layer observed experimentally adjacent to the cladding on the fuel side. Also, minor phases that have been experimentally observed, such as U-Mo, U-Ru, and lanthanoid-noble metals (Nd,Ce-Pd), have been predicted to be stable. As for the U-10Zr fuel, calculations predicted several U-Fe-Zr phases (e.g., FeU6, UFe2, and χ-FeUZr), Fe-(Ce,Nd) phases (e.g., Fe17Ln2), and a FCC phase consisting of Ce, Nd, La, Y, and Sr. These predicted phases are in excellent agreement with experimental observations.